2001 Other Nissan Models rough iddling

I have 2001 nissan quest 62000 miles on it. When you start the car in the morning is ok for almost one minute. The rpms goes to 750 and after a minute they go down to 700. In this point the car start running rough.I also noticed a fluctuation in rpms.
they go to 700 to 750 rpms when iddling in a hot or cold engine.I hooked up the computer and I got 2 codes missfire cilinder #6 and knock sensor malfuction bank 1. I changed all of spark plugs with
originals from dealer, new air filter, new fuel filter, the injecction syst was cleaned. The car stil doing the samething.I put the computer again and now shows only the knock sensor code.
Is the knock sensor the problem? Can you please tell me if can I do something else before I touch the knock sensor? Oh, in my last oil change the mechanic told me about a some hissing noise in engine compartiment. He was checking but could'nt find it.
thank you guys.

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Friday, April 4th, 2008 AT 1:09 PM

1 Reply

MERLIN2021

EXPERT

17,509 POSTS

Knock sensor will retard timming if it's bad or thinks the timming is causing the engine to ping. Too far advanced! Also if there is a hissing You may have a vacuum leak, get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!